Speaker systems and sound chambers therefor



Dec. 24, 1963 R. M. SMITH 3,115,208

SPEAKER SYSTEMS AND SOUND CHAMBERS THEREFOR Filed Sept. 12, 1961 3 Sheets-Sheet l a4 44 FIG. 2 25 4.2% 3 2o 35 g 1%" as a 2 .3; I 29 23 42 g 25 43 53 44 g g 34 mwmmw rmfzw -33 4 FIG. 3 2 INVENTOR.

RICHARD M. SMITH ATTORNEY Dec. 24, 1963 R. M. SMITH SPEAKER SYSTEMS AND SOUND CHAMBERS THEREFOR I5 Sheets-Sheet 2 Filed Sept. 12, 1961 r-so PIC-3.4

FIG. 5

INVENTOR. RICHARD M. SMITH ATTORNEY Dec. 24, 1963 R. M. SMITH SPEAKER SYSTEMS AND SOUND CHAMBERS THEREFOR Filed Sept. 12, 1961 3 Sheets-Sheet 3 1N VENTOR.

RICHARD M. SMI

ATTORNEY United States Patent M 3,115,263 SPEAKER SYSTEMS AND SOUND CHAMBERS THEREFGR Richard M. Smith, 318 6th St, Greenport, NX. Filed Sept. 12, 196i, Ser. No. 137,655 2 Claims. ((Ci. mi -31) This invention relates to improvements in speaker systems, and more particularly in the sound chambers therefor.

Heretofore various types of enclosures for speaker units have been tried, including large flat open baffles, large closed boxes designated the infinite baffle, horn-loaded bafiies, bass-reflex bafiles, combined rear-end front-loaded enclosures, and small sealed boxes. The systems utilizing these various types of enclosure have ranged from massive cabinets which take up valuable room space, to small enclosures which are classed generally as bookshelf speaker systems.

These various types of speaker enclosures are open to various objections, including first cost, replacement cost, space required, tone quality, volume, distortion, limited range, etc.

One object of this invention is a speaker system which is very efficient and which can be marketed in competition with low priced speaker systems now on the market.

Another object is a very efiicient speaker system which occupies negligible floor space, and employs low priced speaker units with results comparable in performance with those obtained with the most expensive speaker systems now on the market.

Another object is to substantially increase the audioirequency range of low priced speaker systems, and/or speaker units.

Another object is to improve the quality and clarity of sound reproduction, and to increase the range of an inexpensive speaker system.

Another object is a low priced speaker system wherein distortion is appreciably reduced.

These and other objects will more fully appear from the detailed description.

in the drawing:

FIG. 1 is a trimetric view of one embodiment of my speaker system with the walls of the enclosure partially broken away to reveal the interior thereof.

FIG. 2 is a cross sectional view of the fragment en closed within the circle in PEG. 1 but somewhat enlarged.

FIG. 3 is a cross sectional view taken along the line 3-3 of FIG. 1, looking in the direction of the arrows.

PEG. 4 is a rear view of the speaker system as viewed along the line i4 of FIG. 3, looking in the direction of the arrows.

FIG. 5 is a cross sectional view taken along the line 5-5 of FIG. 4, looking in the direction of the arrows.

FIG. 6 is a rear view of a modified form of enclosure.

FlG. 7 is a rear view of said modified form with the back panel thereof removed; and

FIG. 8 is a cross sectional view of a fragment taken along the line 88 of FIG. 7, looking in the direction of the arrows.

Like reference characters designate corresponding parts throughout the several figures of the drawing.

The speaker system includes the enclosure 2d which is a rigid box-like structure, having a top wall Zll, a bottom wall 22-, and oppositely disposed end walls 23, 23. If cut from sheet stock, the said walls may be fastened together in any preferred manner as by the nails 24 (FIG. 2), which are preferably provided with barbed shanks to lock the nails in place. The heads of the nails are countersunk and suitably spackled.

The front of the enclosure is open as indicated at 25, but is screened with a conventional grill 2'6 composed of 3,115,208 Patented Dec. 24, 1963 a loosely woven textile fabric which may be secured across the opening 25 in any preferred manner as with a finished molding or otherwise. The rear opening 27 is partially enclosed by a removable imperforate panel 28 which may be secured in place in any preferred manner, as by two or more metal straps 29. Each strap 29 is fastened to the outer face of the panel 28 by two or more wood screws 30 and project beyond the top and bottom edges of the panel 2%, as indicated at El, 31 (FIG. 4), bridging the rear opening 27 and secured to the edge faces 32 of the top and bottom walls by wood screws 33. In the structure shown in FIGS. 1 to 5, the back panel 23 is of smaller dimensions than the rear opening 27, so that when the panel 28 is secured in place in said rear opening, an open space defining an air vent 34 is left between the edge faces of the back panel and the interior faces of the top, bottom, and end, walls 21, 2.2, and 23 of the enclosure 2% A baffle plate 35 extends across the enclosure Ztl critically disposed midway between the open front 25 and the rear opening 27 thereof. Said bafde plate 35 extends from the top Wall 21 to the bottom wall 22, and from one end wall 23 to the other, thus subdividing the enclosure 2.4) into two separate compartments of the same dimensions and of substantially identical volumetric capacities, defining a front loading radiating chamber 36, and a rear loading, non-radiating chamber 37. Openings 38, 33a, sized to accommodate the cone-diaphragms 39 and id of the speaker units 4-1 and 42; respectively, are formed in the baffle plate 35, and the frames which support the speaker units 4-1 and 52 are fastened to the baffle plate 35 in any suitable manner as by the bolts 43, 4-3 and their lock nuts 44, 4d.

The openings 38, 38a constitute sound transmitting passages between the front tone chamber 36, and the rear tone chamber 37, and the cone-diaphragms 3i and 4t) constitute directly radiating closures between said tone chambers, and said cone-diaphragms function in known manner to convert the electrical energy passing through the voice coils (not shown) of the speaker units ll and 42, into acoustical energy. The speaker units may be arranged With their voice coils connected in parallel (FIG. 5), or in series, and the voice coils may be connected over the insulated wires 4-5, 46, 47 to the terminal lugs 43, d9 of a jack 56 mounted in the back panel 28 (FIGS. 4 and 5).

Sound produced by the back of a cone-diaphragm is degrees out of phase from the sound produced by the front of said cone-diaphragm, and theoretically, it is said, that perfect speaker bathing would require that the speaker be placed in the wall between two identical rooms, and that the Wall whereon the speaker was mounted should be insulated against speaker vibration. Under such circumstances all sound from the front of the speaker would go into one room, and all sound from the back of the speaker would go into the other room, and since the volume of air enclosed in each room would be identical, the cushioning eifect on the speaker diaphragm would be the same front and back, so that no mingling of sound would occur and bafiling would be perfect. Recognizing that the foregoing solution is not practicable, it has been suggested as a possible alternative that the speaker might be mounted either on a wall between two fairly isolated rooms, or upon a closet door backed by sound-absorptive clothes, and that the effectiveness of the arrangement last mentioned might be further improved by applying Weatherstripping around the interior of the closet door.

In the speaker system of the present invention, the tone chambers 36 and 37 are of identical dimensions and of substantially identical cubical capacities, the top wall 21, bottom wall 22, end walls 2.3, 23, and the baflle plate 35, are all composed of a solid, self-supporting, load-carrying, sound-absorptive material, and the speaker units 41 and 42 are mounted upon the baiile plate 35, which, being composed of sound absorptive material, effectively insulates the walls of the tone chambers 36 and 37 against any vibration produced at natural resonant frequencies induced by speaker oscillations. Applicants said speaker system therefore closely approaches, and/ or substantially embodies the structure of, the theoretically perfect speaker-bathing system heretofore considered unattainable.

Based upon tests conducted upon speaker systems constructed as herein described out of various sound-absorptive materials it has been determined that enclosures constructed from a sound-absorptive material composed from a base of wood fibres derived by repulping Number 1 grade news stock give excellent results. Said sound-absorptive material is manufactured in the form of building-board by Homasote Company, of Trenton, New Jersey, and is marketed under the name Homasote.

The board material is cut to siz and assembled into the enclosures 2:) in any preferred manner, as by nailing the pieces together with the barbed nails 24 (FIG. 2). A strong and rugged enclosure can be made out of board stock five-eights of an inch thick. The interior walls of the tone chambers and 37 may be painted with a dark paint, and the outside Walls of the box may be painted, or decorated with a contact-material, or While in board form the sound-absorptive material may be veneered in any desired finish as with a hardwood, sheet plastic, formica, or otherwise. It is not necessary to veneer bafiie plate 35.

The performance of a speaker system embodying \my invention and applied to a cabinet of book-self size and equipped with inexpensive cone speakers, compares most favorably with the performance of a large high-priced speaker system of the console type equipped with very expensive cone speakers and operated under the same conditions.

A speaker system of the book-shelf type embodying my invention and employing inexpensive cone speakers mounted in an enclosure constructed of Homasote, said enclosure being sub-divided into the two tone chambers 36 and 37 each having the following inside measurements: 24 inches wide from end wall to end Wall 23, 23; 10 and /3 inches high from top wall 21 to bottom wall 22; and 5 and /8 inches deep from the baffle, or bafile plate 35, to the front opening 25, or to the rear opening 2'7; gives excellent results.

A substantial saving in the cost of production of the enclosures 20 could be made by pouring the repulped material while it is in a plastic condition into a molding apparatus so constructed that the enclosure 29 could be molded in one unit, and the back panel 28 or 25a in a separate piece. The openings 38 and 38a. in the bafiie plate 35, and the openings 34a, 34a in the back panel 28a (FIG. 6), could be formed during molding. Molding would also permit mass production of the enclosures 26, 26a, and of the back panels 28, 28a, and this would result in a substantial saving in cost of production of the cabinets and consequently in the market price of the speaker system.

The speaker units 41 and 4-2 may be adapted to reproduce rnost ehiciently sound waves of difierent audio-frequencies in the desired range, or one of said speaker units may be adapted to reproduce efficiently sound waves over substantially the entire audio-frequency range and the other speaker unit may be adapted to reproduce most er'liciently sound Waves confined within a more limited audio-frequency range. The vented openings 34, and 34a, relieve pressure upon the cone-diaphragms 39, and 49, to eliminate cone-stiliening without damping the oscillations thereof.

What is claimed is:

1. In a sound reproducing apparatus a walled enclosure, all of the walls of said enclosure being rigid and with reh tive high sound absorbing characteristics, a bafiie plate, said bai'fie plate being rigid and with characteristics similar to those of the enclosure walls, said bafile plate extending from Wall to wall across the interior of said enclosure and substantially midway between the opposite ends tiereof and dividing said walled enclosure into two separate distinct and substantially identical acoustical chambers dimension-wise, one of said chambers constituting a front loading radiating chamber and the other a rear loading chamber, said baffle plate having a through opening there in cons-tin 1g a sound transmitting passage between said acoustical chambers, sound producing means mounted upon said batiie plate and including a diaphragm extending across said sound transmitting passage defining an acoustical separation between said acoustical chambers, electromechanical means connected to said diaphragm, a grill extending across a front open end of said front chamber, and a panel mounted on the enclosure walls at a rear end of the rear chamber having air vent means between the panel and the Walls of the enclosure for venting the open end of said rear loading chamber to relieve pressure.

2. The invention as defined in claim 1 wherein the baffle plate has a plurality of spaced openings differing in cross section formed therein, each said opening constituting a separate and distinct sound transmitting passage, the producing means including a plurality of diaphragms one for each passage, each diaphragm adapted to reproduce efficiently sound waves in a particular audio-frequency range, and the cross section of each sound passage correlated to the cross section of the particular diaphragm extending across said sound passage.

References Cited in the file of this patent UNETED STAT ES PATENTS 

1. IN A SOUND REPRODUCING APPARATUS A WALLED ENCLOSURE, ALL OF THE WALLS OF SAID ENCLOSURE BEING RIGID AND WITH RELATIVE HIGH SOUND ABSORBING CHARACTERISTICS, A BAFFLE PLATE, SAID BAFFLE PLATE BEING RIGID AND WITH CHARACTERISTICS SIMILAR TO THOSE OF THE ENCLOSURE WALLS, SAID BAFFLE PLATE EXTENDING FROM WALL TO WALL ACROSS THE INTERIOR OF SAID ENCLOSURE AND SUBSTANTIALLY MIDWAY BETWEEN THE OPPOSITE ENDS THEREOF AND DIVIDING SAID WALLED ENCLOSURE INTO TWO SEPARATE DISTINCT AND SUBSTANTIALLY IDENTICAL ACOUSTICAL CHAMBERS DIMENSION-WISE, ONE OF SAID CHAMBERS CONSTITUTING A FRONT LOADING RADIATING CHAMBER AND THE OTHER A REAR LOADING CHAMBER, SAID BAFFLE PLATE HAVING A THROUGH OPENING THEREIN CONSTITUTING A SOUND TRANSMITTING PASSAGE BETWEEN SAID ACOUSTICAL CHAMBERS, SOUND PRODUCING MEANS MOUNTED UPON SAID BAFFLE PLATE AND INCLUDING A DIAPHRAGM EXTENDING ACROSS SAID SOUND TRANSMITTING PASSAGE DEFINING AN ACOUSTICAL SEPARATION BETWEEN SAID ACOUSTICAL CHAMBERS, ELECTROMECHANICAL MEANS CONNECTED TO SAID DIAPHRAGM, A GRILL EXTENDING ACROSS A FRONT OPEN END OF SAID FRONT CHAMBER, AND A PANEL MOUNTED ON THE ENCLOSURE WALLS AT A REAR END OF THE REAR CHAMBER HAVING AIR VENT MEANS BETWEEN THE PANEL AND THE WALLS OF THE ENCLOSURE FOR VENTING THE OPEN END OF SAID REAR LOADING CHAMBER TO RELIEVE PRESSURE. 